Carbon black



Patented June 10, 1952 CARBON BLACK Wesley C. Ekholm, Monroe, La.,assigner to Columbian Carbon Company, New York, N. Y., a

corporation of Delaware Application December 22, 1949, Serial No.134,520

(Cl. 2li-209.4)

7 Claims. 1

The present invention relates to the manufacture of carbon black andparticularly to the process involving the thermal decomposition of ahydrocarbon by separately injecting it intoa turbulent stream of hotfurnace gases.

In the Wiegand and Braendle Patent No. 2,378,055 there is described animproved process of the type just noted in which a combustible mixtureof a fluid hydrocarbon fueland air is blasted into one end of anelongated, unobstructed chamber to form a turbulent stream of hot blastflame gases. This turbulent stream of blast flame gases courses throughthe furnace chamber and, at a point removed from the point of entry ofthe combustible mixture to the furnace chamber, the hydrocarbon to bedecomposed is separately and forcefully injected into the turbulentstream of gases.

The present invention provides an improvement in the method of operationjust noted and particularly an improved method of effecting the mixingof the hydrocarbon to be decomposed with the hot blast flame gases.

In operations such as specifically illustrated in the patent, thehydrocarbon to be decomposed is injected radially into the furnacechamber, advantageously as relatively small, high velocity streamspositioned directly'opposite one another. Difficulty has beenexperienced in this type of operation where the diameter of the furnacechamber has been too greatly increased. Rectangular furnace chambershave been extensively used in large commercial sized installations, buthere, too, it has been found desirable to limit the width of the chamberto not in excess of about 2 feet, and preferably not greater than about1 foot, in order to maintain a uniform pattern of the streams ofhydrocarbon to be decomposed so as to get uniform mixing of thehydrocarbon with the blast flame gases.

One difficulty of the type noted which has been experienced is that ofspacing the make gas tubes so as to prevent channelling of blast flamegases through the chamber in between the streams of the hydrocarbon tobe decomposed. This difculty has been minimized by close spacing of themake tubes. However, in commercial installations, this solution hasintroduced new problems. The increased number of tubes requires acomplicated manifolding systeml which is serviced with great difficulty.Deposition of carbonaceous residues in the tubes, or in the manifold,tends to disrupt the distribution of make gas to the tubes and resultsin some tubes being overloaded, while others are underloaded.

The present invention provides an improved method of operation wherebymuch of the difficulty heretofore experienced in effecting rapid,uniform mixing of the hydrocarbon to be decomposed With the blast flamegases is avoided.

I have found that these channels of inadequately mixedrblast llame gasesmay be avoided and, at the same time,'the number of make gas streamsreduced by using a reaction chamber of circular section, injecting thecombustible mixture into the reaction chamber as streams moving at highvelocity in a substantially circumferential, or tangential, directionand separately, downstream from the point of injection of thecombustible mixture, forcefully injecting the hydrocarbon to, bedecomposed into the chamber in a substantially radial direction.

By this method of operation, it appears that the blast flame gases tendto follow a more or less helical path through the chamber and,therefore, a path of much greater length, so that for av given timewithin a reaction chamber of a given length much higher blast gasvelocities may be maintained than would be possible if the blast flamegases were passed axially through the chamber. Accordingly, therequirement of careful coordination between furnace diameter and massvelocities is materially relaxed and much greater leeway in the ratio ofblast flame gases to hydrocarbons to be decomposed is permissible.

It appears, therefore, that an advantage of the tangential injection ofthe blast flame gases is that it permits much higher velocities of theblast flame gases than is practical where the blast fiame gases flowsubstantially longitudinally through the chamber.

These higher blast flame velocities make it practical to increase themake gas injection velocities. By reason of the latter, the make gasinjection tubes may be maintained at a lower temperature and a richermake gas may be used without encountering serious coking problems in thetubes. Further, by the use of higher make gas injection velocities, thenumber of make gas injection tubes may be reduced which furthersimplifies construction and maintenance problems.

A still further advantage of the tangential injection of the blast flameis that thereby the blast flame in the region of its initialdevelopment, is in closer contact with the furnace walls than wherelongitudinal blast flame injection is employed. The advantages ofsurface combustion are, in part at least, attained and the permissible'range of ratios of air to natural gas in the combustible mixture ismaterially broadened.

The improved process is applicable to operations in which natural gas,or other normally gaseous hydrocarbons, is decomposed to form the carbonblack. It is, however, especially advantageous in operations adapted toform the carbon black by decomposing a higher molecular weighthydrocarbon, for instance, a petroleum distillatel A particularlydesirable heavier hydrocarbon is a 3 distillate of the type resultingfrom the cracking of petroleum and comprising around 20-60%, usually inthe range of Bil-50% by Weight of aromatic constituents, as determined`by the ytest method D-875-46T of the American Society for TestingMaterials. ltshould most suitably have an aniline cloud point asdetermined by the method prescribed by the said society and designatedD-6lll6T, within the range of 10 to 125 F. Its end point should notexceed 725F. 'and preferably should be somewhat lower.

These higher molecular Weight .hydrocarbons appear to be more readilythermally decomposed than is natural gas, for example, and should bemixed uniformly with the blast name gases proportionately more rapidly.It is desirable, therefore, to accelerate in some way the mixing of thehydrocarbon with the blast gases. This is accomplished in accordancewith the present invention by intensifying the blast gas velocity andturbulence by blasting the combustible mixture into the furnacetangentially, or substantially so, and separately injecting thehydrocarbon to be decomposed substantially radially into theresultingswirling mass of blast flame gases advantageously at a pointVnear the perimeter of the whirling gas stream, i. e., adjacent thefurnace wall,VV thus insuring the Adesired rapid Vand uniform mixing ofthe heavier hydrocarbon with the blast name gases.

In orderfurther to expedite 'the complete dispersion of theheavierhydrocarbon in the blast 'flame gases, I have found it --especiall-yadvantageous to dilute the vaporized heavier hydrocarbon by mixingsteam, air, or other diluent,

therewith, advantageously in proportions within the range-of 1 to 2volumes of steam for each volume of `oil vapor. Mixing of steam with thehydrocarbon to be decomposed has been found particularly beneficial incarrying out the-present process, especially where -it is desired toproduce carbonblack of the type used inthe compounding -of rubber of thetire tread type.V

`According to a preferred aspect of my invention, afpetroleum distillateof the aromatic type just described is vaporized and the vapors mixedwith steam in proportions within the range of vabout .1 'to V2 volumesof steam per volume of :hydrocarbon vapors (eachmeasured at 60 F. and

'760 ,millimeters of mercury) and this mixture is separately `andforcefully injected directly into therapidly swirling flame gases in asubstantially radial direction, With respect to the swirling-motion ofthe blast name gases, and is :thereby substantially instantaneouslydispersed in those blast flame gases and further diluted and therebyheated to the decomposition itemperature of the hydrocarbon.

`Instead of using steam along `as a diluent for the heavier hydrocarbon,natural gas may be used, either together with steam, or alone, as adiluentffor the heavier hydrocarbon. Or, in place of the steam, Vasubstantially inert' gas,

'such as carbon dioxide, or nitrogen, may be employed. `The use of airas a diluent has also been found advantageous` in certain types ofoperation.

The invention will be `further described and illustrated by reference-to Athe accompanying Adrawings which'show conventionally andv somewhatdiagrammatically apparatus found particularly useful in carrying out theprocess and of which:

Figure 1 is a longitudinahsectional vview in elevation of a reactionchamber, together with reaction chamber along the lines 3--3 of Figure1.

In Ythe apparatus shown, the reference nu- Vm'erall .indicates acylindrical, elongated reaction and-cooling 4chamber opening at one endinto a vertical cooler 2. At the lefthand end,

the reaction .chamber is closed by the end block 3, and extendingaxially through this block is a conduit@ adapted to the introduction ofsecondary air into the furnace chamber, as desired.

The chamber I -is formed 4by the cylindrical wall -5 of highlyrefractory material which, .in turn, is covered externally vby layers 6and 1 .of heat insulating material.

Extending through the layers of heat insulating material 'and thefurnace wall Vand substantially normal to the longitudinal axis of thechamber, thereare four blast burner ports 8, eachenteringv the furnacechamber in a circumferential direction, vas more clearly shown in-Figure-2 of the drawings. The apparatus shown is provided with twosubstantially identical sets of these blast burner ports positioned atdifferent distances from the end block 3.

"Further downstream, the furnace chamber is provided with a set of fourradially extending tubes 9V spaced90 apart and extending through thelayers of insulating material and the furnace -Wall as lmore clearlyshown in Figure 3 of the drawings. These tubes are provided for theinjection .into the furnace chamber of the hydrocarbon tombe decomposedand will normally be positioned with their inner ends flush with theinner walls of the furnace chamber. Still further downstream, thefurnace is provided with asecond 4set of hydrocarbon injection tubes 9substantially identical with that just described.

These hydrocarbon injection tubes should be fabricated from highlyrefractory material, for instance, Carbofrax, Alundum, or the like. Theburner ports 8 shouldbefabricated of or lined -with .a similarrefractory material.

'.Spacedalong the vertical .cooler `2 are water sprays In for assistingin cooling `thehot-eflluent furnace gases. Similar sprays kmay bepositioned in thedownstream portion of chamber I adjacent the verticalcooler.

In ,'operation, a combustible mixture of a fluid hydrocarbon fueland airis blasted at high velocity through the circumferential blast burnerports 8, Iis ignited and burned Within the chamber to formra hot, highlyturbulent mass of blastflame gases -rapidly swirling through-the furnacechamber in a more or less helical path. This Ycombustible mixture may-be injected into a zone of .the chamber more or less removed from theend block by selection of one or the other ofthe sets of blast burnerports. The hydrocarbon to -be decomposed -is injected into the `chamberthrough the radial tubes 9 and, as previously described, is extremelyrapidly and uniformly mixed with the swirlingfstreamof blast flamegases,and is heated thereby and decomposed to form carbon 'black insuspension in the .furnace gases. As the suspension continues throughthedownstream fend of Vthe chamber and through the vertical cooler, itis cooled by-'contact with the water sprays l0. Any unvaporizedwaterfromthese sprays, :together with any-carbon knocked uout-of thesuspension, passes downwardly throughthe vertical cooler into the sumpIl and cooled suspension passes from the upper end of the verticalcooler through conduit I2 to conventional separating and collectingapparatus, as well understood in the art. y

The number and diameter of the circumferential blast burner ports havenot been found to be critical so long as they have the capacity forlling the furnace chamber with the violently turbulent blast flamegases. With a furnace chamber approximating 1 foot in diameter, I havefound that a ring of four blast ports, each 2 inches I. D. andpositioned 3 to 6 inches from the inner face of the end block 4 to beadequate for this purpose.

Similarly, the number and size of the hydrocarbon injection tubes aresubject to some variation. Four Carbofrax tubes, 1/2 inch I. D.,positioned as shown in the drawings and located 1 to 4 feet downstreamfrom the blast burner ports have been found highly satisfactory.

In using higher molecular weight hydrocarbons, such as herein described,I have found that the period of time during which the hydrocarbonanddecomposition products thereof should remain in the reaction chamberat reaction temperaturea'in order to result in a carbon black havingcertain desirable rubber compounding characteristics, is less than theso-called contact. time. where natural gas is used as themake 'I'hiscontact time, i. e., the period of time between injection of thehydrocarbon and the quenching of the product to below the reactiontemperature, may be varied by providing a number of spray heads alongthe downstream portion of chamber I and selecting the proper spray, orsprays, so as to cool the suspension at the proper time to below thereactive temperature.

It will be understood, of course, that the contact time is arrived at bycalculation and cannot otherwise be more positively determined in theabsence of more precise information as to the exact path of the gasesthrough the chamber. Contact time so calculated has been found to be arather dependable guide in practical operation.

In general, contact time at temperatures above 2,000 F. should notexceed 0.5 second. Satisfactory operation has been obtained with contacttime within the range of 0.02 to 0.3 second. In these operations, waterspray was used to quench the suspension. It will be understood, however,that waste gases from the process, natural gas or any convenient fluidof relatively low oxidizing potential may be used to effect cooling ofthe suspension.

The blast port velocities at which the combustible mixture enters thefurnace chamber is of primary importance. Velocities within the range ofapproxmiately 60 feet per second to 180 feet per second have beensuccessfully employed. However, port velocities of about 80 feet persecond have been found highly satisfactory in commercial operations.

In the apparatus shown in the drawing, the burner ports are shown to liein a plane perpendicular to the longitudinal axis of the chamber.

AIt will be understood, however, that thesev ports may be directedsomewhat downstream without departing from the spirit of this invention,pro- -vided thexentering combustion mixture is injected into the furnacechamber in a direction substantially circumferential with respect to thechamzbel.;

Likewise, the hydrocarbon injection tubes may be .inclined somewhat fromthe transverse plane of the furnace chamber so long as they are directedsubstantially at the longitudinal axis of the chamber. In the usualoperation of my process, the tube 4 for injection of secondary air isnot employed. However,'operating conditions within the furnace may attimes be more satisfactorily controlled by injecting a relatively smallproportion of the air requirement into the chamber axially throughconduitI 4.

'The process will be further illustrated by the following specificexamples:

Example I The invention has been utilizedA in a furnace constructed asshown in the drawing, and comprising a cylindrical reaction chamber 12inches I. D. and 771/2 feet long, discharging into a vertical spraycooler and having a set of four blast burner ports 2 inches I. D.positioned G-inches downstream from the inlet end of the furnace and asecond identical set of blast burner ports located 9 inches downstreamfrom the first. A ring of four hydrocarbon injection tubes 1/2 inch I.D. was positioned l foot downstream from the second set of blast burnerports and a further identical ring'of hydrocarbon injection tubes waspositioned 3 feet 6 inches downstream from the second set of burnerports. In this operation, the blast air and blast gas was distributeduniformly to two side burners of the rst set and the top and bottomburners of the second set and was supplied at a total rate of 37,000 C'.F. H. of blast air and 3060 C. F. H. of blast gas, the ratio of blastair to blast gas being 12.2. Secondary air was supplied through theconduit 4 at the rate of 2800 C. F. H. Highly aromatic oil was suppliedin vapor form at the rate of 40 gallons per hour and diluted by mixingwith steam at the rate of 860 C. F. H. and injected into the furnacethrough the first set of tubes 9. In this operation, the yield was 2.4pounds per gallon of oil.

The blast gas, i. e., fuel gas, used was natural gas of 960 B. t. u. Thefurnace temperature at a point about 2 feet downstream from the endblock was 2,620 F. The hydrocarbon oil to be decomposed had thefollowing properties:

In substantially identical apparatus, the process was carried on underthe conditions and with the results set forth in the followingtabulation, the temperatures T-l, T-2, T-3, and T4, being taken at thepoints approximately l foot, 2 feet 6 inches, 4 feet 6 inches, and 6feet, respectively, from the inner face of the end block. --In each ofthese runs, the hydrocarbon to be decomposed was injected through thetubes of the rst set only and evenly distributed, the number of tubes ofthe set used in each instance being as indicated in the tabulation. f

Example II VIII Numbercf Tubes Total Blast-Axf-C. E; H SecondaryAirfGjE.H. Total Blast Gas-0. F. H. BlastqRatio-Air: Gas.. l Oil-GalL/HrSteam-Lbs/Hr Steam-Pery GentotOil Vapor Blast Port Ve1octy-ft.lsec. :it60 F. Make Stream Velocity-It/sec, at 60 MakeStream,Velocityfmsceatl600" F Temperatures F.:

-4 Contact time to spray-seconds Yieldv-.Lba/Gal. of Oil RubberProperties:

Gure.Time.,-minutes Modulus at 300% elongation- Tensile StrengthElongation. Hardness- Electrical Resistivity, Log R .Rebound-:.(OptimumCure) The, rubber properties Ygiven'in the4 foregoing tabulation arethose obtained byl compounding therespective blackswith "low temperaturepolymer synthetic rubber by the formula indicatedbelow andvulcanizingthe rubber composition asindicated.

LTP 100.000 Black 50.000 Zincioxide 3.5 Paraux 4-.0 Circosol (2XI-I) 4.0Stearic acid 2.0 Santocure 1*.125 Sulphur 2.0

As illustrative of aromatic hydrocarbonv distillateswhich have been usedwith outstanding.` advantages, there may be noted two types of. oils,the characteristics ofwhich are set forth in the following tabulation.

Sample #1 #2 Gravity (Afl.) 24:5 24.7 AnilinezCloud Point-"F 60. 1 w108Distillation IBPn 348 '480 10% Point.. 406 508 50% Poin '463 '530 90%Point 537 568 End Point 622 588 Recovery, percent. 98.*5' 99.0 Residue,percent 1. 4 0.8 Loss, percent 0.1 0. 2 ASTM D875-46T-Test PercentNaphthencs and Paraiins 32. 32 40. 40 Percent Aromatics- 46.97 40. 71Percent Olefns 20.71: 1S. 89

A@ distillate, such as. sample, 1J was used in;v the foregoing ExamplesIVl V,.and VI and-a.- distillate, such as sample 2, wasused-in-,ExamplesIL III, and VII.

Depending somewhat upon the desiredchar.- acteristics of the carbonblack product, the relative=` proportions of-theblast air, the-hydrocarbon fuel, `the separately injected` hydrocarbon and the secondary airusedlmay bevariedsorne what as illustrated by-the foregoing exam-ples.It will` be understood, of course; that'in alllinstances, the proportionofoxygen:supp'liedwill be substantially `less than that` requiredtorrthe combustion of the -fuelgas -andthelseparatelyinjected hydrocarbon.AThe invention. Ycontemplates operations inwhich theproportion'- offairand gasin the combustiblemixtureLtangentially injected into the chamber;aresuchI as-to-produce eitherffan-oxidiaing, a neutral,or'a.reducing-blast name. The proportions-fof blastlamegases-to theseparately njectedi hydrocarbon, `or mixture of` hydrocarbon, steam, and'the like, maylilcewise be varied somewhat. Theproportion should,ofcourse, in each instancezbe'suchfthait; upon mixing, thev temperatureoff the: resultant mixturewill be atleast suiciently high to veffect thethermal decomposition: off' the; hydrocarbon to carbon black. Wheretheoperationaisrsuch as .to produce anoxidizing. Lblastfiiarne,v,.someiadditional heat may-.be generated upon mixinavr'ith theseparately -inj ected' hydrocarbon by the )come bustionof` a portionthereof.

Itis partieularlyvdesirable that thed-istance between the blast flameinjection point andthe makegas injection point' be-so--correlatedwdththe -ightA angle ofi thelspiralling.- gaslstreaxn, that therespective-make' gasets are directlyin. the path of a fully-developedstreamr of. theV blast gases andi thatA there/be little or nooverlapping of thefmake-gas streams. Thisit'endsftoreduceunevenconcentrations: of? the make easn insthe spirallinggasstream.

In" a preferred method@ ofl operation, vaporized fuel-oil, such as No. 2cycle oilv from' af catalytic cracking'operation, isfvaporized anddiluted with steam, usually inthe-ratio of.' 100to200`per cent, and;normally 125 to 150' percent; bywoluma assuming lf-tcubic feetof;vapors`per-gallonfof the, oil. The. injected' steam vappears tov haveseveraldesirable effects. In the first placmthe presence of steamappears materially, to. reduce thetendency. for carbon depositstdformonvthe heater; wall` and within. the .make gasl injection tubes-and. linesleading, theretoI Secondly,.tl1`e steam, appears` to. act. as an inertdiluent. By regulating. the proportion. of steam,.the. neness of.. theresultant carbon ,particles masa.A to some extent, be controlled. Athird.. advantage de.- r-ived.- from thef usefofsteam` is' that .itVprovides means-fon controlling thetraj ectoryfof.- thefmakegas-:streamss i. e.,' the; extent:- of.. penetration into carbon is thepetroleum distillate of the type elsewhere herein described in detail.

By modifying operating conditions, the characteristics of the resultantcarbon black may be varied over a range extending, for instance, from anormal HMF carbon having a surface area of ve acres per pound, to afurnace black having a surface area in excess cf eleven acres per pound.As normally produced, these blacks, when compounded with an elastomer,produced stocks of very high modulus and unusually high wear resistance.The resultant black, then, as normally produced, is characterized by avery fine particle size with high modulus, or stiffness characteristics.

The invention, in its broader aspect, is independent of contact time.However, in normal operation, a value of about 0.06 second has beenfound adequate for complete reaction, where normally liquid hydrocarbonis used as the primary make, and further time does not appear to benecessary.

` Iclaim:

1. I'he process for producing carbon black comprising in combination thefollowing steps, blasting into one end of an elongated cylindricalreaction chamber a combustible mixture of a fluid hydrocarbon fuel andair in a direction substantially tangential to the inner wall of thechamber, burning the combustible mixture within the chamber to form aswirling stream of blast flame gases passing through the furnace chamberat a temperature in excess of that at which hydrocarbons are decomposedto form carbon black, separately and forcefully injecting into theswirling gases, at a point downstream from the point of entry of thecombustible mixture to the chamber and in a zone near the periphery ofthe swirling gas stream and in a substantially radial direction, astream of hydrocarbons, and thereby immediately subjecting the saidstream of hydrocarbons as it enters the furnace chamber to the impactand shearing forces of the swirling gas stream, whereby the hydrocarbonsthereof are rapidly mixed with the blast flame gases and decomposed byheat absorbed therefrom to form carbon black in suspension in thefurnace gases, cooling the suspension, and separating and recovering thecarbon black therefrom.

2. The process of claim 1 in which the combustible mixture is blastedinto the chamber at a velocity within the range of feet to 180 feet persecond.

3. The process of claim 1 in which the combustible mixture is blastedinto the chamber at a velocity of about feet per second.

4. The process of claim 1 in which the radially injected hydrocarbon isa normally liquid hydrocarbon and is injected into the chamber in avaporized state in admixture with steam.

5. The process of claim 4 in which the steam and hydrocarbon vapors areused in proportions of l to 2 parts of steam for each part ofhydrocarbon vapors by volume.

6. The process of claim 4 in which the injected hydrocarbon is apetroleum distillate composed of aromatic hydrocarbons to the extent ofat least 50% by weight.

7. The process of claim 4 in which the injected hydrocarbon has an endpoint not less than 725 F. and an aniline cloud point within thetemperature range of 10 to 125 C.

WESLEY C. EKHOLM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,163,630 Reed June 27, 19392,375,795 Krejci May 15, 1945 2,378,055 Wiegand et al June 12, 19452,440,424 Wiegand et al. Apr. 27, 1948

1. THE PROCESS FOR PRODUCING CARBON BLACK COMPRISING IN COMBINATION THEFOLLWOING STEPS, BLASTING INTO ONE END OF AN ELONGATED CYLINDRICALREACTION CHAMBER A COMBUSTIBLE MIXTURE OF A FLUID HYDROCARBON FUEL ANDAIR IN A DIRECTION SUBSTABTIALLY TANGENTIAL TO THE INNER WALL OF THECHAMBER, BURNING THE COMBUSTIBLE MIXTURE WITHIN THE CHAMBER TO FORM ASWIRLING STREAM OF BLAST FLAME GASES PASSING THROUGH THE FURNACE CHAMBERAT A TEMPERATURE IN EXCESS OF THAT AT WHICH HYDROCARBONS ARE DECOMPOSEDTO FORM CARBON BLACK, SEPARATELY AND FORCEFULLY INJECTING INTO THESWIRLING GASES, AT A POINT DOWNSTREAM FROM THE POINT OF ENTRY OF THECOMBUSTIBLE MIXTURE TO THE CHAMBER AND IN A ZONE NEAR THE PERIPHERY OFTHE SWIRLING GAS STREAM AND IN A SUBSTANTIALLY RADIAL DIRECTION, ASTREAM OF HYDROCARBONS, AND THEREBY IMMEDIATELY SUBJECTING THE SAIDSTREAM OF HYDROCARBONS AS IT ENTERS THE FURNACE CHAMBER TO THE IMPACTAND SHEARING FORCES OF THE SWIRLING GAS STREAM, WHEREBY THE HYDROCARBONSTHEREOF ARE RAPIDLY MIXED WITH THE BLAST FLAME GASES AND DECOMPOSED BYTHE HEAT ABSORBED THEREFROM TO FORM CARBON BLACK IN SUSPENSION IN THEFURNACE GASES, COOLING THE SUSPENSION, AND SEPARATING AND RECOVERING THECARBON BLACK THEREFROM.